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Cationic polyacrylamide copolymers (PAMs): Environmental half life determination in sludge‑treated soil

Kationische Poly(acrylamid)-Copolymere: Halbwertszeitbestimmung in der Umwelt in Klärschlamm-behandeltem Boden
: Hennecke, Dieter; Bauer, Angela; Herrchen, Monika; Wischerhoff, Erik; Gores, Friedhelm

Fulltext urn:nbn:de:0011-n-4971443 (1.3 MByte PDF)
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Created on: 20.6.2018

Environmental Sciences Europe : ESEU 30 (2018), Art. 16, 13 pp.
ISSN: 2190-4715
ISSN: 2190-4707
Journal Article, Electronic Publication
Fraunhofer IAP ()
Fraunhofer IME ()
transformation; sludge-amended soil; outdoor lysimeter study; labelled polymer; molar mass analysis; polymer degradation

Cationic polyacrylamide copolymers (PAMs) are used for sludge dewatering in municipal waste water treatment and might enter the environment by spreading of the sludge on agricultural land. Concern has been expressed since little is known about the degradation of PAMs in soils. To obtain detailed information on the polymers fate in the soil compartment, the degradation of 14C-radiolabelled PAM in an outdoor lysimeter was studied. No plant uptake and leaching of radioactivity was observed. There was practically no vertical movement of polymer and no transformation products found at the end of the study. For the top 10 cm soil layer, a mass balance was established throughout the study. About 10% of applied radioactivity was not extractable from soil even with a matrix destructive meth od, and this was concluded to be bound residue. Characterization of extractable radioactivity by means of GPC-analysis showed a significant decrease of the molecular weight of the PAM with time. The decrease in molecular weight indicates a breakdown of the polymer backbone (the CC-chain), and is assumed to be primary degradation. The total radioactivity content in the 10 cm top soil layer was quantified every 6 months over a period of 3 years. The results show a significant decrease of the total radioactivity over time and this is defined as ultimate degradation following the definition of OECD and EPA. Based on the data, a half-life time of 2.0 × 103 days and a rate constant of 0.00035/day were calculated. With a χ2 of 12.0 the results of the calculation are thus valid and reliable. The rate constant indicates a mineralization of 22.5% within a period of 2 years based on the total recovered radioactivity. This half-life time is solely based on mineralization and does not take into account the degradation of the polymer backbone, hydrolysis of the side chains, incorporation into the soil matrix, and thus is a conservative approach. 14C-PAM degrades very slowly in soil after land-spreading as a component of sewage sludge. Even in a very conservative evaluation which only considered the loss of radioactivity, a half-life time of 5.4 years was determined.